Recently, the development of new renewable energy has become more important and interested due to the serious environmental pollution and the lack of fossil fuel. Among the new renewable energy, a solar cell is spotlighted as a pollution-free energy source for solving the future energy problem because it rarely causes environmental pollution and has the semi-permanent life span and there exists infinite resources for the solar cell.
Solar cells may be defined as devices to convert light energy into electrical energy by using a photovoltaic effect of generating electrons when light is incident onto a P-N junction diode. The solar cell may be classified into a silicon solar cell, a compound semiconductor solar cell mainly including a group I-III-VI compound or a group III-V compound, a dye-sensitized solar cell, and an organic solar cell according to materials constituting the junction diode.
A solar cell made from CIGS (CuInGaSe), which is one of group I-III-VI Chal-copyrite-based compound semiconductors, represents superior light absorption, higher photoelectric conversion efficiency with a thin thickness, and superior electro-optic stability, so the CIGS solar cell is spotlighted as a substitute for a conventional silicon solar cell.
In general, a CIGS solar cell can be prepared by sequentially forming a back electrode layer, a light absorbing layer and a front electrode layer on a glass substrate. Meanwhile, according to the related art, doped zinc oxide (AZO) used for the front electrode is thickly deposited under lower power to reduce resistance, so the light transmittance may be lowered, the process may be unstable, the material cost may be increased and the facility investment cost may be increased. In addition, serial resistance Rs of the front electrode may be increased as the width of the solar cell is enlarged, so that the electric conductivity may be lowered.